1. Field of the Invention
The present invention relates to a system for controlling an idle speed of an internal combustion engine in accordance with a change in load due to an air conditioner.
2. Description of the Related Art
Operation of an air conditioner can make the idling operation of an internal combustion engine unstable. In order to prevent the idle speed of the engine from being made unstable by operation of the air conditioner, there is proposed an idle control system which controls the idle air amount so as to ensure a prescribed idle speed in accordance with the load of the air conditioner by regulating the air flow bypassing the throttle valve.
This conventional idle speed control system performs a feedback control to reduce a deviation of a sensed actual idle speed from a desired idle speed which is predetermined as a target. An idle speed control system of this type is shown in Japanese Patent Publications No. Heisei 05-33770 and No. Heisei 05-99046.
In the idle speed control system of such a conventional type, a torque correction quantity based on actual discharge pressure of the compressor of the air conditioner is performed so as to maintain a stable idling condition in spite of the load change of the air conditioner. In this system, the torque correction quantity changes in proportion to actual discharge pressure as actual discharge pressure increases during an air conditioner ON transient.
This conventional system, however, cannot avoid suffering from a temporary decrease of the idle speed due to a delay in response of the engine, even if the torque correction quantity, based on the actual discharge pressure of the compressor, is made quickly.
Therefore during a large change of the load, fluctuation of the idle speed increases and stability of the idle speed becomes worse.